A Democratic senator asked the White House on Monday to explain why the name of an imprisoned Al Qaeda (search) terror suspect was disclosed to reporters even as the suspect was cooperating secretly by sending e-mails to terrorists so authorities could trace their locations.

Sen. Charles E. Schumer (search) of New York asked the White House homeland security adviser, Frances Townsend, to identify who provided to reporters last week the name of Mohammed Naeem Noor Khan (search) and why Khan's name was disclosed. Schumer also asked whether Townsend believed the disclosure had compromised national security.

"I believe that openness in government is generally the best policy, but the important exception should be anything that compromises national security," Schumer wrote in his letter to Townsend. He cited press statements by authorities in Pakistan and England that the disclosure was harmful to their investigations.

National security adviser Condoleezza Rice (search) acknowledged Sunday in a televised interview that Khan's name had been disclosed to reporters in Washington "on background," meaning that it could be published, but the information could not be attributed by name to the official who had revealed it.

"The problem is that when you're trying to strike a balance between giving enough information to the public so that they know that you're dealing with a specific, credible, different kind of threat than you've dealt with in the past — you're always weighing that against kind of operational considerations," Rice said on a Sunday morning cable news show.

"We've tried to strike a balance," Rice added. "We think for the most part, we've struck a balance, but it's indeed a very difficult balance to strike."

The U.S. government's disclosure on Aug. 1 of Khan's arrest and some of the information tied to Khan came amid a furious defense by the Bush administration explaining its decision to warn one day earlier about possible attacks against U.S. financial buildings in New York, Washington and Newark, N.J.

White House spokesman Scott McClellan cautioned Monday that information may be more limited about future raids against Al Qaeda suspects.

"It is important that we recognize that sometimes there are ongoing operations under way," he said. "And as we move forward on capturing or bringing to justice Al Qaeda members, we need to keep that in mind. And sometimes we aren't able to go into as much detail we would like to because of those ongoing operations."

Khan, arrested July 13 in Pakistan, was described by authorities as a communications technician working for Al Qaeda who helped send electronic messages on behalf of the group's members.

U.S. and Pakistani officials, speaking on condition of anonymity, have confirmed that Khan agreed after his arrest to send e-mails to Al Qaeda members, and Khan received replies from at least some of them. Days after Khan's arrest, British authorities arrested 12 terror suspects in raids, including one person described as a senior al-Qaida operative, Abu Eisa al-Hindi, and Khan's cousin, Babar Ahmad.

U.S. officials and government interviews with other captured terror suspects indicated al-Hindi was sent to the United States in early 2001 by the principal architect of the Sept. 11 suicide hijackings to perform surveillance on economic and "Jewish" targets in New York.

Ahmad has been indicted in the United States on charges he tried to raise money for terrorism from 1998 through 2003. Authorities said he had battle group plans for Navy vessels in the Persian Gulf.